1. Field of the Invention
The present invention relates to a method and an apparatus for purification of the exhaust gases arising from incineration plants, metal refining factories, oil refineries and others.
2. Description of the Prior Art
The combustion of coal or petroleum is accompanied with the exhaust of noxious substances, and the waste gases or soot and smoke discharged from some chemical plants or metal refining factories also contain noxious substances. When the content of these noxious substances in the air comes to exceed a certain limit, it poses a serious problem from the viewpoint of environmental pollution, factory management and so forth.
As the substances causing the pollution of air, there are (1) noxious gases such as SO.sub.2 and SO.sub.3 arising from the combustion of sulfur compounds or the combustion of sulfur components of fuels, NO and NO.sub.2 originating from the combustion, oxidation, etc. of nitrogen contained in fuels, CO arising from the incomplete combustion of carbon contained in fuels, as well as ammonia, hydrocarbons and the like, (2) the floating soot or dust consisting of fine particles of carbon or ashes arising from the combustion operation, (3) the falling soot or dust consisting of particles less fine than the floating soot or dust, and others.
As means for removing these polluting substances contained in the exhaust gases, in the case where said polluting substance is a noxious gas, (a) a method of purifying said gas by absorbing it with a proper absorbent, (b) a method of absorbing said gas onto the surface of a porous material such as active carbon, silica gel, activated alumina and the like or (c) a method of directly burning and oxidizing said gas thereby to decompose or convert it into a harmless gas or oxidizing it at a relatively low temperature by the use of a proper catalyst is applicable, while in the case where said polluting substance is soot or dust, a method of removing it by the use of a dust-catching apparatus is applied. In performing the dust-catching, the force of gravity, inertia, centrifugal force, cleansing, filtration, electricity, sound wave, etc. are utilized, and, to cite the most popular dust-catching apparatuses, there are Venturi scrubbers, bag filters, electric dust-catchers, centrifugal separators, etc.
The purification of exhaust gases has hitherto been conducted by applying the foregoing methods and apparatuses either individually or by combining them appropriately, but the purification efficiency of such conventional means has not been satisfactory.